1. Field of the Invention
The present invention relates to a sheet transport apparatus in which register spaces to correct skew of a sheet are provided in a sheet transport path.
2. Description of the Related Art
In an image formation apparatus such as a copier and printer and an image reading apparatus provided in a scanner, facsimile or the like, provided is a sheet transport apparatus which feeds an original (sheet) to each processing section such as a printing section and reading section, and discharges the sheet processed therein. Such a sheet transport apparatus is configured as a transport unit attachable to the image formation apparatus or image reading apparatus having a reading platen to read an image of the sheet.
In the sheet transport apparatus, a sheet transport path is curved in the shape of a U and extends so as to connect between a paper feed tray provided on the upper-stage side and a sheet discharge tray provided on the lower-stage side, and the reading section having the reading platen exists in the path therebetween. A plurality of transport rollers is disposed in the sheet transport path. These transport rollers are provided with a separate roller that separates a plurality of sheets mounted on the paper feed tray, register roller that corrects skew of a sheet, a pair of reading rollers arranged to sandwich the reading section, sheet discharge roller that transports the read sheet toward the sheet discharge tray, etc. A sheet transport apparatus for reading the frontside and backside of a sheet successively is provided with a reverse path and reverse roller that reverse a sheet with the frontside read and then transport the backside toward the reading section.
The sheet transport apparatus provided with the aforementioned reverse mechanism is comprised of a first transport path extending to the sheet discharge tray from the paper feed tray via the reading section to read the frontside of a sheet, and a second transport path for reversing the sheet with the frontside read and re-transporting the backside toward the reading section. Then, the second transport path joins the first transport path on the upstream side of the reading section.
Sheet transport apparatuses disclosed in Japanese Patent Application Publication No. 2003-63687 and Japanese Patent Application Publication No. 2003-95490 have a first register space in the first transport path extending from the paper feed tray to the register roller, and a second register space in the second transport path for transporting the sheet that is reversed via the reading section again toward the reading section. Further, first to third switching members are arranged to be swingable in portions in which the first transport path joins the second transport path in between the register roller and the transport roller, and a clearance to correct skew of the sheet is formed in between the guide surface of the switching member and the guide surface of the sheet transport path.
In the sheet transport apparatuses disclosed as described above, since the second register space to correct skew of the reversed sheet is in a position away on the upstream side of the register roller, there is the fear that skew of the sheet newly arises for a period during which the sheet reaches the reading section via the register roller. Further, since the sheet passing through the first transport path and the second transport path is transported while swinging the switching member, friction increases and sometimes interferes with transport of the sheet. Particularly, in sheets made of a thin material, there is the risk of causing a sheet jam. Therefore, it is necessary to adjust the clearance between the guide surface of the switching member and the guide surface of the transport path as appropriate, while setting the curvature of each guide surface accurately, and the apparatuses thus have the inconvenience in adjustment or setting.
Therefore, it is an object of the present invention to provide a sheet transport apparatus for correcting skew of a sheet in the upstream vicinity of the reading section and thereby enabling reading processing to be performed accurately and smoothly in any case of sheet frontside reading transport and backside reading transport.